The dexterity of a robotic manipulator has been defined as the ability of a manipulator to access a point in a workspace from different directions and orientations. Numerically controlled machines generally require an end effector of the manipulator to follow a specified trajectory. This trajectory requires the end effector to visit various points in Cartesian space from arbitrary directions which requires the manipulator to have six degrees of freedom, three for position and three for orientation.
In a fiber placement machine, the position of the end effector is generally provided by two slides and a forearm that either pivots or slides while the orientation of the end effector is provided by a wrist that connects a head carrying the end effector to the end of the forearm. Positioning of the head and end effector in a fiber placement machine is not difficult. However, orientation of the end effector carried by the head is difficult because the end effector that applies the fiber to a tool or form has a substantial width so that the band of fibers is twisted as it travels from the forearm to the head via the wrist. Because of this phenomenon, existing fiber placement machines have limited dexterity. This is particularly true in a fiber placement machine that lays a fiber band of tows that must be kept separate as they travel from the forearm to the head.
U.S. Pat. No. 4,872,619 granted to Milo M. Vaniglia Oct. 31, 1989 discloses a redirect apparatus of a fiber placement machine having a fiber placement head 25 that is attached to a forearm 14 by a wrist 15. The wrist 15 is a serial roll wrist that is disclosed in U.S. Pat. No. 4,068,536 granted to Theodore Hahn Stackhouse Jan. 17, 1978. A fiber band of tows is delivered from a creel assembly 24 to the fiber placement head 25 via a grooved roller 29 and two redirect rollers 30. Redirect rollers 30 are mounted on casters supported on a stationary creel bracket 31 and an outboard support bracket 32 of fiber placement head 25 respectively. The fiber band of tows is twisted between the grooved roller 29 and the first redirect roller 30 supported on the stationary creel bracket 31 and again between the two redirect rollers 30. The redirect rollers 30 may be part of assemblies 38a, 38b that include a servo-motor 403 to provide positive controlled movement to the roller assembly. See also U.S. Pat. No. 4,877,193 granted to Milo M. Vaniglia Oct. 31, 1989 and U.S. Pat. No. 4,943,338 granted to Jerry B. Wisbey et al. Jul. 24, 1990.
This arrangement has a relatively low dexterity primarily because the fiber band of tows is offset from the centers of rotation of each of the wrist axes. This offset causes the fiber band of tows to orbit the center of rotation rather than merely to twist about it, thereby increasing the angle by which the fiber band of tows deviates from perfect perpendicularity with the axis of rotation of the redirect rollers. Additionally, this arrangement requires that all three degrees of freedom through which the fiber placement head can be oriented must be accommodated by the relative position of redirect rollers 30 (mounted on stationary creel bracket 31) and redirect rollers 30 (mounted on outboard support bracket 32 on the fiber placement head 25). These two conditions together limit the range through which the wrist can be oriented without applying excessive side angle to the fiber band of tows. It can be seen that the greater the offset of the fiber band of tows from the centers of rotation, the more limited the range of orientation of the wrist will be.
U.S. Pat. No. 5,022,952 granted to Milo M. Vaniglia Jun. 11, 1991 discloses another arrangement for a fiber placement machine comprising a tiltable forearm or housing 70 that has a fiber placement head 130 attached to a rotatable arm 72 by a roll bend roll type of robotic wrist 128. A fiber band of tows 11 is delivered from a creel assembly carried by the tiltable housing 70 via a fixed position roller 136 and two tape redirect rollers 138 and 140 of the same type that are discussed above in connection with U.S. Pat. No. 4,872,619 granted to Milo M. Vaniglia Oct. 31, 1989. As indicated above, the fiber band of tows 11 is twisted between the fixed position roller 136 and the first redirect roller 138 supported on the tiltable housing 70 and again between the two redirect rollers 138 and 140. As above, the redirect rollers 138 and 140 may be part of assemblies that include a servo-motor to provide positive controlled movement to the roller assembly.
While this arrangement has been used successfully for many years this arrangement also has a relatively low dexterity primarily because the fiber band of tows is offset from the centers of rotation of each of the wrist axes. This offset causes the fiber band of tows to orbit the center of rotation rather than merely to twist about it, thereby increasing the angle by which the fiber band of tows deviates from perfect perpendicularity with the axis of rotation of the redirect rollers. Additionally, this arrangement requires that all three degrees of freedom through which the fiber placement head can be oriented must be accommodated by the relative position of redirect rollers (mounted on stationary creel bracket) and redirect rollers (mounted on outboard support bracket on the fiber placement head). These two conditions together limit the range through which the wrist can be oriented without applying excessive side angle to the fiber band of tows. It can be seen that the greater the offset of the fiber band of tows from the centers of rotation, the more limited the range of orientation of the wrist will be.
U.S. Pat. No. 5,110,395 granted to Milo M. Vaniglia May 5, 1992 discloses a fiber placement head 12 that has upper and lower idler rollers 92 and 94 that separate every other tow between a redirect roller 90 and a compaction shoe 104.
U.S. Pat. No. 5,239,457 granted to Richard L. Steidle et al Aug. 24, 1993 discloses a redirect roller control for a fiber placement machine that controls the swivel angles of the two redirect rollers that are disclosed in the fiber placement machines described above in connection with U.S. Pat. No. 4,872,619 granted to Milo M. Vaniglia Oct. 31, 1989 and U.S. Pat. No. 5,022,952 granted to Milo M. Vaniglia Jun. 11, 1991.